nv50/nvc0: Build codegen in nv50.

This is required to make libnv50 independent of libnvc0.
Remove hacks for static Makefiles

v2: Andreas Boll <andreas.boll.dev@gmail.com>
    - don't remove compatibility with scripts for the old build system

v3: Andreas Boll <andreas.boll.dev@gmail.com>
    - remove more obsolete hacks

v4: Andreas Boll <andreas.boll.dev@gmail.com>
    - add a previously removed TOP variable to fix vgapi build
glapi/gen: remove an obsolete comment from Makefile.am
mesa/dricore: Drop compatibility for the old Mesa build system and -avoid-version.
Drop last parts of compatibility for the old Mesa build system.
gallium/auxiliary: Build libgallium shared.
configure.ac: Save user {C,CXX}FLAGS and append them at end.

This way the user has the privilege of last decision and so the option to build an optimized debug build again.
Suppress clang's warnings about unused CFLAGS and CXXFLAGS.
tests: AM_CPPFLAGS must include $(top_srcdir) instead of $(top_builddir).
gtest: Build it only for 'make check'.
radeon, clover: Make it compile on LLVM >= r171366.
r200: Fix probable thinko in r200EmitArrays

Effectively this path would always assert.  Move the break statement to
the (probable) intended place.

Note: This is a candidate for the stable branches.

Signed-off-by: Adam Jackson <ajax@redhat.com>
mapi: Build libglapi always shared.
mesa: Build libmesa shared.
Install all internal shared libs to $(libdir)/mesa-$VERSION.
Makefile.am: s:-no-undefined:-Wl,--no-undefined to make it work.
gallium/drivers: Build libs -shared.
xmlpool: Fix out-of-tree builds.